mmc: block: do not assign mq_rq when aborting command
The code in mmc_blk_issue_rq_rq() aborts a command if the request
is not properly aligned on large sectors. As part of the path
jumping out, it assigns the local variable mq_rq reflecting
a MMC queue request to the current MMC queue request, which is
confusing since the variable is not used after this jump.